There are urgent requirements to avoid vehicle accidents due to driver's errors in order to improve traffic safety. In view of these requirements, there are known technologies for detecting, based on observed values indicative representing the running conditions of a vehicle or the driver's operating conditions of the vehicle, driver's abnormal behaviors, one of which is disclosed in, for example, Japanese Patent Application Publication No. 2009-154675.
The technology disclosed in the Patent Publication uses normal behavior models and abnormal behavior models. Each of the normal behavior models represents a model obtained by modelling driver's driving behaviors when they are normal. Each of the abnormal behavior models represents a model obtained by modelling driver's driving behaviors when they are abnormal, which include, for example, a driver's driving behavior when the driver is dozing off.
Specifically, the technology cyclically collects observed values of the running conditions of a vehicle or the driver's operating conditions of the vehicle. Then, the technology estimates, based on the previously obtained observed values and the normal behavior models, a current observed value as a first estimation value, and estimates, based on the previously obtained observed values and the abnormal behavior models, a current observed value as a second estimation value.
Then, the technology determines whether a current observed value, which is actually observed, is closer to one of the first estimation value and the second estimation value than to the other thereof, and determines whether the driver's driving behaviors are normal or abnormal.